Digital intercom network over dc-powered microphone cable

ABSTRACT

A digital intercom system provides DC power and multi-channel bidirectional digital communications over existing cabling such as microphone cabling used in analog intercom networks. Three or more conductors in the cabling are used for both transmitting and receiving digital signals and carrying DC power. The digital intercom system includes digital user stations and a digital master station which can be used to retrofit an existing analog intercom network or deployed in a new network. User stations can be connected to the cabling via drop cables which do not use active electronic components. The master station routes digital audio and control data packets in three or more channels based on respective network addresses of the user stations to provide point-to-point, point-to-multi-point, and party line communications among the user stations. Sessions and groups can be configured which define talker and listener user stations.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to technology for an intercom network.

2. Description of the Related Art

Intercom systems are widely used in various venues to allowcommunications between users. For example, personnel at performing artvenues such as theaters and concert halls, as well as televisionstudios, sports events, houses of worship, and schools, often useintercom equipment to communicate with each other. The personnel talk toeach other via portable user stations (e.g., belt-pack devices connectedto a headset), which rely on a master station to control and power theintercom system.

Traditionally, intercom systems have used analog signaling over cablingto communicate voice and control data between user stations. A two-wireparty line system utilizes two wires of a cable, such as a microphonecable, to allow users to listen concurrently to a single conversation. Afour-wire matrix system utilizes a transmit pair and a receive pair forthe audio to and from a user station to provide point-to-pointcommunications. In practice, cables with six to eight wires may be usedin an intercom system in which two or four wires carry data and theremaining four wires carry audio. In each case, an additional groundwire or shield is also typically provided.

Recently, digital intercom systems have been developed in which userstations are connected via computer networking components such as CAT-5cable. CAT-5 cable is commonly used in a structured wiring system inwhich cables are installed in a building in a permanent manner. However,such digital intercom systems do not allow the easy retrofitting ofexisting analog intercom networks with digital equipment to provide fullfeatured, multi-channel digital communications over existing cabling.

SUMMARY OF THE INVENTION

A digital intercom system is provided which includes multiple userstations connected to one or more master stations. The digital intercomsystem can be retrofitted to an existing analog intercom network ordeployed in a new network.

In one embodiment, a digital intercom network includes a cable networkhaving at least one cable. The at least one cable has first, second andthird conductive paths, where the third conductive path is a groundpath. The network further includes at least one user station connectedto the first, second and third conductive paths. Further, a masterstation includes: (a) a DC power supply connected to the first, secondand third conductive paths, where the DC power supply powers the atleast one user station, (b) a transceiver which provides bidirectionaldigital communications in at least three channels via the first, secondand third conductive paths, including transmitting digital signalsconcurrently via the first, second and third conductive paths, andreceiving signals concurrently via the first, second and thirdconductive paths, and (c) a router in communication with thetransceiver, where the router routes digital data packets in the atleast three channels.

In another embodiment, a master station in a digital intercom networkhas a first connector which is connected to at least first, second andthird conductive paths of at least one cable of the digital intercomnetwork, where the third conductive path is a ground path. A DC powersupply is connected to the at least first, second and third conductivepaths via the first connector, where the DC power supply powers at leastone user station which is connected to the at least one cable. Atransceiver provides bidirectional digital communications with the userstations in at least three channels via the at least first, second andthird conductive paths, including transmitting digital signalsconcurrently via the at least first, second and third conductive paths,and receiving signals concurrently via the at least first, second andthird conductive paths. A router is in communication with thetransceiver, where the router routes digital data packets in the atleast three channels to provide digital point-to-point, digitalpoint-to-multi-point, and digital party line communications among theuser stations.

In another embodiment, a user station for use in a digital intercomnetwork provided over at least one cable includes an interface to the atleast one cable, where the at least one cable has at least first, secondand third conductive paths, and the third conductive path is a groundpath. A power conversion unit is associated with the interface forreceiving DC power from the at least first, second and third conductivepaths. A transceiver provides bidirectional digital communications viathe at least first, second and third conductive paths, includingtransmitting digital signals concurrently via the at least first, secondand third conductive paths, and receiving signals concurrently via theat least first, second and third conductive paths. The bidirectionaldigital communications are provided via at least one channel of at leastthree available channels which are provided over the at least first,second and third conductive paths.

In another embodiment, a method is provided for retrofitting an analogintercom network to provide a digital communication capability, wherethe analog intercom network includes user stations, an analog masterstation and a cable network having at least one cable. The at least onecable has first, second and third conductive paths, where the thirdconductive path is a ground path. The method includes disconnecting theanalog user stations and the analog master station from the at least onecable, connecting digital user stations to the at least one cable inplace of the analog user stations, and connecting a digital masterstation to the at least one cable in place of the analog master station.The digital master station: (a) provides DC power to the at least first,second and third conductive paths, the DC power is sufficient to powerthe user stations, and (b) provides bidirectional digital communicationsin at least three channels via the first, second and third conductivepaths, including transmitting digital signals concurrently via thefirst, second and third conductive paths, and receiving signalsconcurrently via the first, second and third conductive paths, where theproviding bidirectional digital communications includes routing digitaldata packets at the digital master station in the at least threechannels to provide digital point-to-point, digitalpoint-to-multi-point, and digital party line communications among theuser stations according to respective network addresses of the userstations.

Corresponding methods, systems and computer- or processor-readablestorage devices which have executable code for performing the methodsprovided herein may also be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a depicts exemplary digital intercom networks with respectivemaster stations.

FIG. 1 b depicts exemplary digital intercom networks served by a commonmaster station.

FIG. 2 a depicts an exemplary three-conductor microphone cable which canbe used in a digital intercom network to carry DC power and digitalsignals.

FIG. 2 b depicts a cross sectional view of the cable shown in FIG. 2 a.

FIG. 2 c depicts an exemplary five-conductor microphone cable which canbe used in a digital intercom network to carry DC power and digitalsignals.

FIG. 2 d depicts a cross sectional view of the cable shown in FIG. 2 c.

FIG. 3 a depicts an exemplary connection which connects athree-conductor drop cable of a user station to a main cable.

FIG. 3 b depicts an exemplary connection which connects a five-conductordrop cable of a user station to a main cable.

FIG. 4 depicts an exemplary daisy-chain connection of a cable to a userstation.

FIG. 5 depicts exemplary differential mode signals.

FIG. 6 a depicts an exemplary block diagram of one embodiment of a userstation.

FIG. 6 b shows a coupling network of a user station or master stationconnecting to a five-conductor cable.

FIG. 6 c depicts an exemplary block diagram of another embodiment of auser station.

FIG. 6 d depicts the Ethernet MAC and PHY layers of the OSI protocolstack.

FIG. 7 a depicts an exemplary back panel of a digital master station.

FIG. 7 b depicts an exemplary front panel of a digital master station.

FIG. 8 a depicts an exemplary block diagram of a digital master station.

FIG. 8 b depicts an exemplary block diagram of a power line interface ofFIG. 8 a.

FIG. 9 a depicts an exemplary routing table, and FIGS. 9 b and 9 cdepict routing of a packet between user stations using the routing tableshown in FIG. 9 a.

FIG. 10 a depicts another exemplary routing table, and FIG. 10 b depictsrouting of a packet between user stations using the routing table shownin FIG. 10 a.

FIG. 11 a depicts an exemplary table of listener intercoms, and FIG. 11b depicts forwarding of a packet using the table.

FIG. 12 a depicts an exemplary first process for selectivelycommunicating data packets among user stations.

FIG. 12 b depicts an exemplary second process for selectivelycommunicating data packets among user stations.

FIG. 12 c depicts an exemplary third process for selectivelycommunicating data packets among user stations.

FIG. 13 depicts an exemplary process for retrofitting an analog intercomnetwork to provide a digital communication capability.

DETAILED DESCRIPTION

The present invention provides a digital intercom system in which amaster station provides DC power over a network to user stationsconnected to the network, and facilitates multi-channel digitalcommunications among the user stations over the same twisted wire pairin a cable. In one embodiment, the network allows many separate channelsof audio communications, along with control data and power, to bedelivered to multiple user stations over a cable in a daisy-chain(series-connected) configuration. Further, user stations can easily andinexpensively be connected to the cable via a passive connection such asa Y- or T-connection.

The digital intercom system provided herein can mimic the analogparty-line concept where all user stations (e.g., belt packs, remotestations, wall-mount stations, etc.) are ‘commoned’ together along asingle cable (typically XLR3 microphone cable) with each user stationreceiving its power and audio on this single cable. A basic party-lineinfrastructure might have all user stations connected via adaisy-chained configuration where the output of one user station isconnected (such as by an XLR3 connector) to the input of the next userstation and so on. However, in practice, the physical cabling is oftenrouted within a venue's walls or through conduit, in which case usersconnect to the intercom system much like one would connect an electricaldevice to a power outlet.

The physical cabling is an important consideration when designing aparty-line intercom system, but in both of the described cablingscenarios, all users are grouped in a ‘party-line’ call (where all userscan talk/listen to all users). Multiple party-lines (channels: A, B, C .. . ) can operate simultaneously within a given intercom system in orderto organize and isolate communications between functional groups(talent, stagehands, video/audio, etc.). Most live performance venueswill cable the infrastructure so that all channels are available atbulkhead junction boxes spaced periodically throughout the facility;internal y-split cables ensure a closed circuit. The primary tenets ofan analog party-line system are its robustness, reliability, ease ofset-up, voltage and audio down the same cable, and relatively low cost.

A digital intercom system can replicate the desirable tenets of theanalog party-line system while improving its shortcomings with digitaltransmission. In a digital intercom system herein, each user station isindividually addressable. This removes the traditional party-linedependence of having the audio channel intimately related to itsassociated power line. Put another way, users can be physicallyconnected in a daisy-chain fashion (User 1, 2, 3, . . . 10) along thesame cable, yet could be grouped into different party-lines or functiongroups. This approach is expected to provide significant benefits tousers by simplifying cable runs while maintaining communicationsflexibility similar to a point-to-point matrix intercom solution.

Moreover, the digital intercom system is simple to setup, re-configureand operate having a similar ease of installation of its analogcounterpart, i.e., it is a “plug-and-play” solution which allows easyretrofitting of an existing analog intercom network. Any needed systemconfiguration can be performed directly on the master station. Agraphical user interface (GUI), which can be Internet browser-based, maybe provided for system configuration, with standard communication portslocated on the front of the master station to connect with a personalcomputer (PC) or personal digital assistant (PDA) via a common interfaceprotocol such as USB.

The system may be fault tolerant such that the failure of adaisy-chained element (e.g., a user station isdropped/breaks/turned-off) should not affect the ability to communicatewith other user stations connected to the network. That is, a physicalpass-through function can be provided. Further, the platform canadvantageously operate over standard single screened twisted pairmicrophone cable and can be tolerant to short circuits so that in theevent of cable damage only the affected segment of the cable will losethe ability to transmit audio. Similarly, a cable break should onlyaffect downstream elements. In some embodiments, the system can have anoptional fly-back connection (an additional cable that allows a ringnetwork to be formed) for power and data redundancy so that the systemcan continue to function in the event that the main cable is severed.

Individual user stations should be able to easily access any one of themultiple (predetermined) party-lines via a simple key and display whichare selectable on the user station. These functions should also belockable to prevent communications errors from users inadvertentlyselecting the wrong party-line or accessing channels without permission.

FIG. 1 a depicts exemplary digital intercom networks 100 and 101 withrespective master stations 136 and 140, which have the above-mentionedfeatures. The networks 100 and 101 are connected to one another, and canassume a variety of topologies and include multiple master stations andassociated user stations and cable links. A basic topology includes amaster station and a number of user stations which are connected by acable network, and which communicate with one another via the masterstation. The master station and user stations are nodes in the network.For example, in the network 101, a master station 140 is connected toassociated user stations 156, 160, 164 and 168. The master station istypically placed at a fixed location in a facility and receives powerfrom the AC mains wiring of the facility. The AC power is converted toDC power and provided to the user stations. The master station 140 mayoptionally be manned by an operator who has the ability to talk andlisten in the network, including communicating selectively with one ormore user stations. Further, the master station 140 may communicate witha digital interface 142 to send and receive audio and other data to andfrom other networks. The user stations may be portable, user-worndevices, such as belt pack devices which allow a respective user to talkand listen to other users connected to the same network. The userstations include a microphone and speaker which may be built in orconnected such as in a plug-in headset. Depending on configurationsettings, the master station and each user station are able to talk toand/or listen to any other user in the system, either individually or ingroups.

The master station 140 is connected to the user stations 160, 164 and168 in a daisy-chained configuration. Specifically, the master station140 is connected to the user station 160 via cable 152, connection 150and cable 158. The user station 160 is connected to the user station 164via a cable 162, and the user station 164 is connected to the userstation 168 via a cable 166. Further, the master station 140 isconnected to the user station 156 via a drop cable 154 and theconnection 150, which essentially provides a passive Y- or T-connectionwhich does not use active electronic components. The cables 152, 158,162 and 166 form a primary branch of a cable network of the network 101.FIG. 1 a illustrates an optional fly back cable 170 connecting the lastuser station 168 in the daisy-chain to the master station 140, forming aring network topology between master station 140 and user stations 160,164 and 168. A ring topology allows the master station 140 to deliverpower to each of the user stations and communicate audio and other data,even in the event that one of the cables 152, 158, 162 and 166 becomesdamaged or disconnected.

FIG. 1 a indicates that the master station 140 may also communicate witha second master station 136 in a second network 100 via a line 138 suchas a copper or fiber Ethernet connection. More than two master stationscan be connected together in a system as well. For example, a fiber linkcan provide transmission for up to about 10 km, while a CAT-5 cable canprovide transmission for about 100 m. Multiple master stations may beused in a large facility such as a sports stadium to provide sufficientcoverage throughout the facility. The link 144 from the master station140 to the digital interface 142 may similarly use a copper or fiberEthernet connection.

FIG. 1 a also indicates that a variety of network topologies may beused. In the network 100, the master station 136 communicates via acable 132 with a passive bulkhead 122, which in turn communicates with auser station 106 via a drop cable 108 and a user station 102 via a cable104. The passive bulkhead 122 provides a passive connection which doesnot use active electronic components. The passive bulkhead 122 isconnected via a cable 124 to another passive bulkhead 126. User stations110 and 112 are connected to bulkhead 126 via cable 120, connection 118and cables 114 and 116. The passive bulkhead 126 is connected via acable 128 to a wall-mount station 130, from which a fly back cable 134returns to the master station 136 for redundancy.

The physical cabling can be routed freely within a venue, or routedwithin a venue's walls or through conduit, in which case users connectto the intercom system much like one would connect an electrical deviceto a power outlet. For example, user stations can be connected to dropcables which are plugged into junction boxes along a main cable line.

FIG. 1 b depicts exemplary digital intercom networks served by a commonmaster station. Here, the master station 140 serves both the network 101and one or more additional networks, such as a network 103. The network103 includes cables 153, 155, 159, 163 and 171, connection 151 and userstations 157, 161 and 165. The master station may have multiple pairs ofXLR connectors in its back panel for connecting to the cables of themultiple networks, as discussed further in connection with FIG. 7 a.Further, the internal processing and routing circuitry of the masterstation can allow digital communications among user stations in the sameor different networks.

FIG. 2 a depicts an exemplary three-conductor microphone cable 200 whichcan be used in a digital intercom network to carry DC power and digitalsignals. The microphone cable is a multi-conductor cable used in theintercom network, and can advantageously be of a type which is commonlyused in analog intercom networks to allow easy retrofitting of suchnetworks to provide a digital communications capability. For example,commonly used microphone cable includes three conductors: namely a firstconductor “1” which connects to a ground shield, a second conductor “2”which is a positive DC voltage terminal and carries a positive ornegative data signal on an associated wire, and a third conductor “3”which is a negative DC voltage terminal and carries a negative orpositive data signal which is a mirror image of the positive or negativesignal, respectively, on the second conductor. This is a differentialmode transmission scheme, discussed further below in connection withFIG. 5. Thus, audio and control data can be carried via the first,second and third conductors. The first conductor provides a groundreference for the second and third conductors, so that voltages on thesecond and third conductors are defined with respect to the ground.

The cable 200 includes a main portion 202 and a connector 203. A commontype of connector is an XLR connector which can have pins or socketsconnected to two or more wires and a surrounding ground shield. Theconnector can be male or female, having pins or sockets 204, 206 and 208named “1,” “2” and “3,” respectively.

The three-pin XLR connector (referred to as XLR3) is commonly used as abalanced audio connector for connections between microphones and audioequipment. EIA Standard RS-297-A describes the use of XLR3 for balancedaudio signal applications. Other types of XLR connectors exist. Afour-pin XLR cable is commonly used for intercoms and handsets, camerasand analog lighting control components. A five-pin XLR cable is commonlyused for digital lighting control components, dual-element microphonesand dual-channel intercom headsets. A six-pin XLR cable is commonly usedfor dual-channel intercom belt packs. Any of these types of XLR cablescan be used for digital communications, although only two of the wiresplus the ground shield are needed to provide digital communicationsamong a set of devices using the techniques described herein.Conceivably, a first pair of wires can be used to provide digitalcommunications among a first set of devices, and a second pair of wirescan be used to provide digital communications among a different, secondset of devices. Possibly, some devices can communicate over both pairsof wires. Additional pairs of wires could also be used for digitalcommunications. Other wires may be used for other purposes. It is evenpossible to provide both digital and analog communications in the samecable.

In one implementation, digital communications among the user stationsare provided using conductors/wires which are connected to pins “2” and“3.” Other wires may be present in the cable but are not used forproviding digital communications among the user stations, in thisexample. The three conductors are sufficient to provide several channelsof bidirectional digital communications in a network, as well asproviding DC power sufficient to power a number of user stations. Thenumber of user stations that can be powered by a single master stationdepends on the power consumed by each user station and the supply powerof the master station, as well as losses due to factors such as thecable gauge and length of the cable. In some embodiments, the masterstation may supply 60-96 W. For example, with a supply power of 60 W and5 W used by each user station, up to twelve user stations can be powered(ignoring cable losses). In contrast, other approaches such as Powerover Ethernet (PoE) power a single device and do not allow poweringmultiple devices from a common power supply node and signal path.

FIG. 2 b depicts a cross sectional view of the cable shown in FIG. 2 a.The basic construction of a cable for low-impedance microphone orbalanced line applications is the shielded twisted pair. Such a cableincludes signal- and power-carrying copper conductors 213 and 215 asrespective wires which are insulated by insulation 207 and 209,respectively, and twisted together in a filler 214. Conductor 213 isconnected to pin 206, and conductor 215 is connected to pin 208. Acopper ground shield 212 is connected to the ground conductor 204. Theshield acts as a shield to RF interference as well as serving as aground reference. An outer jacket 210 surrounds the copper ground shield212.

FIG. 2 c depicts an exemplary five-conductor microphone cable which canbe used in a digital intercom network to carry DC power and digitalsignals. In an alternative approach, auxiliary conductors are providedso that power and signals are carried over five or more conductivepaths. This allows power to be delivered over a longer cable. Forexample, in a cable 250 with a cable portion 251, a connector 252, andpins or sockets 253-257, pin “1” 253 can be the ground path, pins “2”and “3” can be connected to the positive DC voltage terminal of thepower supply, and pins “4” and “5” can be connected to the negative DCvoltage terminal of the power supply.

FIG. 2 d depicts a cross sectional view of the cable shown in FIG. 2 c.The cable portion 251 includes copper conductors 266, 264, 269 and 262as respective wires which are insulated by insulation 267, 265, 270 and263, respectively, and provided in a filler 261. In one approach, theconductors associated with pins “2” and “4” can be a twisted pair, andthe conductors associated with pins “3” and “3” can be another twistedpair. Conductor 266 is connected to pin 254, conductor 264 is connectedto pin 255, conductor 269 is connected to pin 256, and conductor 262 isconnected to pin 257. A copper ground shield 268 is connected to theground conductor 253. An outer jacket 271 surrounds the copper groundshield.

FIG. 3 a depicts an exemplary connection which connects athree-conductor drop cable 154 of a user station 156 to a main cableline, which includes cables 152 and 158. As mentioned previously inconnection with FIG. 1 a, connections such as 118 and 150 can be used toconnect a drop cable or spur to a main cable line. Advantageously, suchconnections are passive and do not use active electronics such as atransceiver (transmitter/receiver) or repeater. In contrast,conventional Ethernet communications such as over CAT-5 cable usepoint-to-point links which extend between active electronic devices suchas hubs, switches, routers or computers. Such communications do not bothtransmit and receive using the same conductor, but have a dedicatedtransmit pair and a receive pair. Significant cost savings andflexibility are realized by avoiding the need for active electronicdevices.

The cables 152 and 158 of FIG. 1 a, which are part of a main branch orline of the cable network 101, are connected via the connection 150,such as by XLR connectors. The drop cable 154 allows the user station156 to tap into the signal and power carried by the cables 152 and 158,and may also use an XLR connector. In FIG. 3 a, the cable 152 includes acable portion 302 and a connector 304, the cable 158 includes a cableportion 332 and a connector 334, and the drop cable 154 includes a cableportion 352 and a connector 354. Moreover, the cable 152 includesconductive paths 308, 310 and 312 which correspond to conductors 206,208 and 204, respectively, of FIG. 2 a. Similarly, the cable 158includes conductive paths 338, 340 and 342 which correspond toconductors 206, 208 and 204, respectively, of FIG. 2 a, and the dropcable 154 includes conductive paths 358, 360 and 362 which correspond toconductors 206, 208 and 204, respectively, of FIG. 2 a. Conductive paths308 and 338 join to form a continuous conductive path through multipleable portions, as do conductive paths 310 and 340, and 312 and 342. Inthe connection 150, the conductive paths 308, 338 and 358 areelectrically connected to a connection point 324, the conductive paths310, 340 and 360 are electrically connected to a connection point 326,and the conductive paths 312, 342 and 362 are electrically connected toa connection point 328.

As a result, the power and signal provided by the master station areprovided on the drop cable, so that the user station 156 can receivepower and digital communication signals via the drop cable 154.Similarly, a digital communication signal transmitted by the userstation 156 on the drop cable is provided on the cables 152 and 158, sothat the master station and other user stations can receive a signalfrom the user station 156.

FIG. 3 b depicts an exemplary connection which connects a five-conductordrop cable of a user station to a main cable. The user station canobtain power and transmit and receive digital signals via five (or more)conductive paths in a cable. This allows power to be delivered over alonger cable. The like numbered elements of FIG. 3 b are repeated here.The cables used in this embodiment correspond to those in FIGS. 2 c and2 d. Cable 152 includes an auxiliary conductive path 309 to theconductive path 308, and an auxiliary conductive path 311 to theconductive path 310. Cable 158 includes an auxiliary conductive path 339to the conductive path 338, and an auxiliary conductive path 341 to theconductive path 340. Drop cable 154 includes an auxiliary conductivepath 359 to the conductive path 358, and an auxiliary conductive path361 to the conductive path 360. Connection point 325 connects theconductive paths 309, 339 and 359. Connection point 327 connects theconductive paths 311, 341 and 361. The other conductive paths areconnected as described in connection with FIG. 3 a.

FIG. 4 depicts an exemplary daisy-chain connection of a cable to a userstation. The cables 158 and 162, and user station 160, of FIG. 1 a aredepicted in further detail. In this case, the cables may be plugged intocorresponding connectors, such as XLR connectors, in the user station160. The cable 158 includes a cable portion 402, a connector 404, andconductors 408, 410 and 412 which correspond to conductors 206, 208 and204, respectively, of FIG. 2 a. The cable 162 includes a cable portion432, a connector 434, and conductors 438, 440 and 442 which correspondto conductors 206, 208 and 204, respectively, of FIG. 2 a. A couplingnetwork or component 420 in the user station 160 includes connectionpoints 424, 426 and 428 to which conductors 452, 454 and 456 in the userstation 160 are electrically connected to the corresponding conductorsin the cables 158 and 162. The conductors 452, 454 and 456 lead toprocessing circuitry in the user station 160.

FIG. 5 depicts exemplary differential mode signals. As mentioned, apositive DC voltage terminal of a power supply can be connected to onewire in a cable, and a negative DC voltage terminal of the power supplycan be connected to another wire in the cable. Further, a positive ornegative voltage data signal can be provided in either wire. When apositive voltage signal is provided in one wire, a mirror image negativevoltage signal is provided in the other wire. This is a differential orbalanced mode transmission scheme. For example, a positive DC voltage,VDC+, of +30 V, may be used in conjunction with a negative DC voltage,VDC−, of −30 V. Thus, the potentials are equal in magnitude but oppositein polarity. Further, the supply voltages are modulated so that themagnitude varies with time to represent voice and other data. Thesetime-varying signals are represented by waveforms 500 and 510, which areequal in magnitude but opposite in polarity. For example, in athree-conductor cable, the waveform 500 can be carried by the conductorassociated with pin “2” in FIG. 2 a, and the waveform 510 can be carriedby the conductor associated with pin “3” in FIG. 2 a. In afive-conductor cable, the waveform 500 can be carried by the conductorsassociated with pins “2” and “3” in FIG. 2 c, and the waveform 510 canbe carried by the conductors associated with pins “4” and “5” in FIG. 2c. A difference between the waveforms 500 and 510 represents voice andcontrol data which is carried via the cable. In practice, digitalsignals of about 1-2 V can be carried atop a DC power rail of 30-60 V.Other levels can be used as well.

Both conductors (pins “2” and “3”), or both sets of conductors (a setwith pins “2” and “3”, and a set with pins “4” and “5”), carry the DCpower with balanced data superimposed, such that theinformation-carrying signal is represented by the difference between thetwo waveforms. For example, waveforms at +30 V and -30 V at one point intime result in a signal of +60 V, and waveforms at +31 V and -31 V atanother point in time result in a signal of +62 V.

FIG. 6 a depicts an exemplary block diagram of one embodiment of a userstation 600 (corresponding, e.g., to user station 160 in FIG. 1 a). Auser station can be portable and user-worn or carried, such as on a beltpack, or non-portable, such as in a console mount, rack mount, deskmount or wall mount. A portable user station can include a connector toa headset. A user station 600 provided herein advantageously has theability to participate in a digital intercom network which supportsmultiple channels (e.g., three or more channels) to provide digitalpoint-to-point, digital point-to-multi-point, and digital party linecommunications. In particular, the user station includes circuitry whichallows it to send and receive digital data packets, as well as to drawDC power, from the same set of conductors.

The user station shown in FIG. 6 a allows a user to communicate with anyother user/channel/subgroup connected to the digital intercom network.The user station is individually addressable according to a uniqueaddress/identifier associated with the user station, and allowspoint-to-point communication as well as conventional party-lineoperation. The user station has a set of controls which allow the userto select a channel. Although, a lockout feature may be implemented toprevent users from changing/selecting any pre-set configurations of theuser station, including the ability to select channels. The user stationhas the simplicity of operation experienced by users of analog userstations but can achieve improved audio performance and flexibilityincluding multi-channel access.

In particular, the signal- and power-carrying conductors 602, 604 and605 of a cable 601 are accessed via conductive paths 606, 607 and 608,respectively, by a coupling network 610. The coupling network 610provides line driving and transient protection. A power supply unit 612is connected to the coupling network 610 to access the DC power which iscarried by the cable 601. The power supply unit 612 typically transformsthe voltage, e.g., 30-60 V DC, to lower levels which may be required bythe circuitry of the user station 600. Note that the user station 600can be used for both portable and non-portable devices. However, theelectrical load to a non-portable station such as a wall-mount speakerstation and/or a desktop speaker station will be different than that ofa portable station such as a belt pack due to the different microphoneand speaker. Further, a wall-mount or desktop speaker station may belocally powered, in which case a user station does not need to drawpower from the cable 601 to operate.

In one possible implementation, a chipset 614 implements the MediumAccess Control (MAC) layer and the Physical (PHY) layers of theInternational Organization for Standardization/Open System Interconnect(ISO/OSI) stack. These are the bottom two layers of the stack. Thechipset 614 is a transceiver as it sends and receives signals on thenetwork. Specifically, the transceiver provides bidirectional digitalcommunications in at least three channels via the first, second andthird conductive paths 602, 604 and 605, including transmitting digitalsignals concurrently via the first, second and third conductive paths,and receiving signals concurrently via the first, second and thirdconductive paths. The transmitting and receiving can occur concurrentlywith respect to one another, or at different times.

The MAC layer interfaces with the PHY layer through a Medium-IndependentInterface (MII). A typical 10/100 PHY Ethernet implementationincorporates separate 10BaseT and 100BaseTX interfaces. Further detailsare provided in FIG. 6 d. The chipset 614 also provides an Analog FrontEnd (AFE) which provides a tuner and analog-to-digital converter (ADC).The chipset 614 can incorporate a microcontroller, Ethernet MAC, andPHY. An example of such a chip set is the INT6400 256 LFBGA (Low-ProfileFine-Pitch Ball Grid Array) package available from INTELLON CORPORATION,Orlando, Fla., USA. This chip is suitable for communicating over ACpower lines using the HomePlug AV standard for home networking ofcomputers. It is optimized for multi-media streaming applications and isfully compliant with the HomePlug AV standard with 200 Mbps PHY-rateover power line wiring.

The chipset 614 can include a complete HomePlug AV MAC and PHY, anEthernet MII, an external SDRAM (synchronous dynamic random accessmemory) interface, along with interfaces for two external SPI (serialperipheral interface) devices. The chipset 614 can also include theINTELLON i60 Line Driver IC.

In further detail, the PHY provides 200 Mbps OFDM@1024-QAM, and supports1024/256/64/16/8-QAM, QPSK, BPSK and ROBO Modulation Schemes. The PHYuses 128-bit AES Link Encryption with key management for securepowerline communications. Windowed Orthogonal Frequency DivisionMultiplexing (OFDM) with noise mitigation improves data integrity innoisy conditions. Moreover, dynamic channel adaptation and channelestimation maximizes throughput in harsh channel conditions. Finally,Advanced Turbo Code Forward Error Correction is used. The MAC providesintegrated Quality of Service (QoS) features such as contention-freeaccess, four-level priority-based contention access, and multi-segmentbursting. The MAC also provides Type of Service (ToS), Class of Service(CoS) and Internet Protocol (IP) port number packet classifiers, andsupports Internet Group Management Protocol (IGMP) managed multicastsessions. IGMP is a communications protocol used to manage themembership of Internet Protocol multicast groups. IGMP is used by IPhosts and adjacent multicast routers to establish multicast groupmemberships.

Peripherals of the chipset 614 can include a General-PurposeInput/Output (GPIO), 32 bit Peripheral Component Interconnect Expressversion 2.2 (PCI2.2), MPEG Transport Stream (TS) Serial interface andJTAG test/In-Circuit Emulator (ICE) port.

The user station may also have a USB port to receive configurationcommands from a computer when the particular user station is beingconfigured, e.g., with a network address or group or session informationwhich determines which user stations the particular user station cancommunicate with.

The chipset 614 may access flash memory 618 and a SDRAM or SRAM 616. Thechipset 614 further communicates with a Digital Signal Processor (DSP)624 via a path 634 and a Dual Inline Memory Module (DIMM) connector 622.The DSP can be provided as a card, as shown, or fitted directly to aprinted circuit board (PCB). The path 634 is connected to a reverse MIIinterface to the Ethernet MAC of the chipset 614. The DSP 624 routesaudio and control data which are received at the user station 600 fromthe cable, or generated at the user station for transmission on thecable 601. Specifically, the DSP 624 sends (via path 636) control datato and receives control data from, an Inter-Integrated Circuit (I²C)chip 632, which in turn communicates with LEDs and I/O buffers 630 toreceive and send control data. The DSP 624 also sends (via path 638)digital audio to and receives digital audio from an audio codec 628,which in turn communicates with audio buffers/switches 626 to receivetalk audio from a microphone and send listen audio to a speaker. Thecodec (coder/decoder) 628 provides analog-to-digital conversion of talkaudio and digital-to-analog conversion of listen audio. It is alsopossible to fit separate ADCs and DACs in place of the codec. The DSP624 may use time-division multiplexing (TDM) in communicating with theaudio codec 628.

FIG. 6 b shows a coupling network of a user station or master stationconnecting to a five-wire cable. The coupling network 610 of FIG. 6 amay connect to a five-conductor cable as an alternative to athree-conductor cable. In this configuration, auxiliary signal- andpower-carrying conductors 613 and 615 are provided in the cable 601, inaddition to the conductors 602, 604 and 605. The auxiliary conductors613 and 615 are accessed via conductive paths 609 and 611, respectively,by the coupling network 610. A similar approach can be used for acoupling network of a master station.

The chip set 614 as a transceiver provides bidirectional digitalcommunications using one signal on both a first conductive path 604 andits auxiliary conductive path 613, and another signal on both a secondconductive path 605 and its auxiliary conductive path 615.

FIG. 6 c depicts an exemplary block diagram of another embodiment of auser station (corresponding, e.g., to user station 160 in FIG. 1 a). Inthis implementation of a user station 652, the analog front endfunctionality is separated out to an AFE chip 650 which works with a MACand PHY chip 654. The chip 654 does not include a reverse MII interfaceto the Ethernet MAC. Instead, two Ethernet PHY chips 642 and 646 areused to communicate audio and control data between the DSP 624 and thechip 654. In particular, the chip 654 communicates via a MII on line 648with Ethernet PHY chip 646, the Ethernet PHY chip 646 communicates withthe Ethernet PHY chip 642 using Ethernet on line 644, and the EthernetPHY chip 642 communicates with the DSP 624 via a MII on line 640. Anexample of the chip 654 is the SPC200e in a 512 Enhanced Plastic BallGrid Array (EPBGA) package available from SPIDCOM TECHNOLOGIES S.A.,Bourg La Reine, France. The SPC200e has been used for in-home broadbandcommunication over electrical power lines and coaxial cables, such asfor Internet and VoIP, Video on Demand, IPTV, and whole in-house HDTV.The SPC200e does not require a zero crossing reference.

An example of the AFE 650 is the AD9865, available from ANALOG DEVICES,INC., Norwood, Mass., USA. The AD9865 is a mixed-signal front end IC fortransceiver applications requiring Tx and Rx path functionality. Thus,the AFE 650 includes a transceiver. An alternative for the chip 654 isthe CG3111, with the CG3112 for the chip 650, both available fromCOPPERGATE COMMUNICATIONS, INC., Newark, Calif., USA. This approachrequires two Ethernet PHYs or a reverse MII. Another alternative for thechip 654 is the DSS9101, with the DSS78002 for the chip 650, bothavailable from DS2, Valencia, Spain. This approach has a reverse MIIinterface to the Ethernet MAC and therefore does not require twoEthernet PHYs.

FIG. 6 d depicts the Ethernet MAC and PHY layers of the OSI protocolstack. As mentioned, one possible technique for digital communication inan intercom network uses Ethernet MAC and PHY to implement the bottomtwo layers of the ISO/OSI stack. The stack 660 includes a hardware layer662, including a physical (PHY) layer 666 and a data link layer 664which may use media access control (MAC). Software layers 670 include anetwork layer 672 which may use the Internet Protocol (IP), a transportlayer 674 which may use the Transmission Control Protocol (TCP) or UserDatagram Protocol (UDP), a session layer 676 which may use a RemoteProcedure Call (RPC) protocol, a presentation layer 678 and anapplication layer 680

In further detail, the data link layer 664 includes a transmittercomponent 684 and receiver component 685 and associated buffers 682 and683, respectively. A flow control component 681 and a MII managementcomponent 686 are also provided. The MII 687 of the data link layerinterfaces with the MII 688 of the physical layer. The physical layeralso includes a transmitter component 691 and receiver component 692, inaddition to an encoding component 693, loop back support 689 andphase-locked loops 690. A typical 10/100 PHY Ethernet implementationincorporates separate 10BaseT and 100BaseTX interfaces, where 10BaseTuses Manchester encoding, and 100BaseTX uses 4B/5B encoding.

The Ethernet standard is defined by IEEE 802.3. The Ethernet MACimplements a data-link layer, supporting operation at both 10 Mbits/sand 100 Mbits/s. The standard typically implements the MII, also definedin IEEE 802.3. It includes a data interface and a management interfacebetween the MAC and the PHY. The data interface includes a channel forthe transmitter 684 and a separate channel for the receiver 685. Eachchannel has its own clock, data, and control signals. With themanagement component 686, upper layers can monitor and control the PHY.The PHY is the physical interface transceiver and implements thephysical layer.

FIG. 7 a depicts an exemplary back panel 700 of a digital master station(corresponding, e.g., to master station 140 in FIG. 1 a). The back panel700 includes a number of connectors for audio, control data and power.The particular connectors depicted, along with their number andplacement on the master station, are examples only and are not intendedto limit the scope of the technology described herein. In one approach,both digital and audio networks can communicate with one another via themaster station. The connectors can include a pair of RJ45 sockets 702and 704 for 100/10 BaseT Ethernet communications such as might be usedfor the path 138 between the master stations 136 and 140 in FIG. 1 a. Apair of 4-wire RJ45 sockets 706 and 708 provides an interface to two4-wire audio circuits, such as for communicating via CAT-5e or CAT-6cable. RJ45 connectors 705 and 707, or, alternatively, fiber opticconnectors, can be used for communications with other remote devices. Apair of three-pin female XLR connectors 710 and 712 can be used for ananalog party line option.

A power socket 714 receives main power such as at 100-240 V, with aninput frequency range of 50-60 Hz. A GPIO connector 716 allowsconnection of switch inputs (e.g., a footswitch to operate front panelcontrols instead of pressing a front panel button) and relay outputs(e.g., to turn on a light or close a door at the press of a front panelbutton).

Either of connectors 720 and 724 may be used individually or as a pairto provide DC power and digital communications as described herein on amain cable power line in a digital intercom network. The connectors 720and 724 are three-pin male XLR connectors, in one possible approach. Forexample, the connector 720 may connect to one end of a cable or seriesof cables while the connector 724 connects to the other end of the cableor series of cables, to provide a ring topology with redundancy, e.g.,as shown in networks 100 and 101 of FIG. 1 a. The connector 720 may be afirst connector which is connected to one end of at least one cable,while the connector 724 may be a second connector which is connected theother end of the at least one cable, to form a closed ring. For example,in the network 101 of FIG. 1 a or 1 b, the first connector 720 canconnect to the cable 152 and the second connector 724 can connect to thecable 170. DC power and digital communications can be provided via eachconnector 720 and 724. Similarly, an additional pair of connectors 722and 726 may be used to provide DC power and digital communications dataon an additional cable network ring. For example, in the network 103 ofFIG. 1 b, the connector 722 can connect to the cable 153 and theconnector 726 can connect to the cable 171. The two rings maycommunicate with one another via a switch in the master station,discussed below in connection with FIG. 8 a. The back panel 700 furtherincludes a stage announce/public address output 728, a program input 730for monitoring a program source and a hot mic output 732.

FIG. 7 b depicts an exemplary front panel 740 of a digital masterstation. The front panel 740 includes displays and controls which assistan operator in controlling the digital intercom network. A headsetoutput connector 742 and microphone input connector 744 are provided. AUSB connector 750 (standard, micro and/or mini) provides connectivity toa computer which provides a GUI regarding a master station status, andto receive configuration commands. A set of user interface elements suchas buttons 746 provide additional controls such as mic on-off, headsetselect, talk to announcer, remote mic kill, all talk,loudspeaker/headphone level and program sound level. A set of keysets745 are also provided. Each keyset has a display (752, 762, 772, 782) toinform the operator of a currently selected user station or group ofuser stations being monitored, a talk button (754, 764, 774, 784), acall button (756, 766, 776, 786) and a volume control (758, 768, 778,788).

FIG. 8 a depicts an exemplary block diagram of a digital master station.The digital master station 800 serves as a central hub to coordinate thecommunication of digital packets among the user stations, in addition toproviding DC power to the user stations. The circuitry of the masterstation may be provided on one or more printed circuit boards within ahousing. In an example implementation, a switch 810 such as 8-port FastEthernet and 2-port MII switch 810 coordinates the movement of dataamong different components of the master station. 100/10 BaseT moduleconnectors 802, 804, 806 and 808 are option module connectors which maycommunicate with the back panel connectors 702, 704, 706 and 708,respectively, and with the switch 810, to send and receive data. Powerline interfaces 812 and 814 also communicate with the switch 810 to sendand receive data. The power line interfaces 812 and 814 include powerprotection, and Ethernet transmit/receive capability. The power lineinterfaces 812 and 814 deliver DC power and transmit/receive digitalcommunications signals to one or more cables of the digital intercomnetwork via the connectors on the back panel of the master station. Forexample, power line interface 812 is associated with XLR connectors 720and 724, and power line interface 814 is associated with XLR connectors722 and 726. The power line interfaces provide a capability which issimilar to that of the user stations as discussed previously inimplementing the MAC and PHY layers of the protocol stack in addition toproviding an analog front end. See FIG. 8 b for further details.

A router 816, which may be implemented as a DSP, also communicates withthe switch 810. The router provides a routing and forwarding capabilityfor digital data packets in the network over three or more channels, asdescribed further below in connection with FIGS. 10 a-12 c. Ethernet100/10 BaseT module connectors 818 and 820, which are Ethernet fiber orcopper interfaces, also communicate with the switch 810.

A DSP 830 also communicates with the switch 810, and includes a memory.The DSP 830 interacts with a GPIO component 816, which is associatedwith the back panel connector 716, and with keyset components 845, userinterface elements 846, and USB interface 850, which are associated therespective front panel components 745, 746 and 750, respectively. TheDSP 830 can communicate Ethernet packets to the switch 810.

A codec 840 communicates with a number of components includingconnectors 830 and 832 which are associated with the program in(broadcast) connector 730 and the hot mic out connector 732,respectively, on the back panel. The codec 840 also communicates withcomponents 828, 842 and 844, which are associated with the stageannounce output 728, the headset out connector 742, and the mic inconnector 744, respectively on the front panel. The codec 840 can alsodrive a loudspeaker 843. There is analog circuitry (not shown) betweenthe codec 840 (or ADC/DAC combination) and the input/output connectors.

An internal power supply unit (PSU) 854 and a power conversion component856 are also provided. The master station is powered by a mains supply(100-240V) and has internal power supplies converting that to a DCvoltage. There are then further on-board power supply circuitsconverting that DC level to the supply voltages needed by the circuitry.The master station can provide an output at the back panel connectorswith an appropriate voltage, current and power.

The router 816 provides a routing and forwarding capability for digitaldata packets in the network, to provide digital point-to-point, digitalpoint-to-multi-point, and digital party line communications among theuser stations according to their respective network addresses. Varioustypes of routing techniques can be used. An example routing technique isprovided in PCT patent publication WO2009/015460, published Feb. 5,2009, titled “Multi-Point To Multi-Point Intercom System,” byTalk-Dynamics Corp., Montreal, Canada, which is incorporated herein byreference. In this technique, intercom terminals are registered astalking or listening intercom terminals in an intercom session table. Anintercom server sends to the listening intercom terminals some or all ofthe unmixed audio packets received by a talking intercom terminalaccording to an intensity signal value located in the header of theunmixed audio packets. Talk-Dynamics provides low-latency (5-10 ms) IPtechnology that is capable of connecting 100+ users in a conference callin the V-SERIES user panel, manufactured by CLEAR-COM, VITEC GROUPCOMMUNICATIONS, LLC, Alameda, Calif., USA. Other routing techniques maybe used as well.

FIG. 8 b depicts an exemplary block diagram of a power line interface ofFIG. 8 a. As mentioned, the power line interfaces 812 and 814 of FIG. 8a provide a capability which is similar to that of the user stations asdiscussed previously in implementing the MAC and PHY layers of theprotocol stack in addition to providing an analog front end. Each of thepower line interfaces can include any of the chips mentioned previously,for instance. For example, the power line interface 812 can include thechip set 614, flash memory 618 and SDRAM or SRAM 616, in addition to acoupling network 850 which includes the XLR connectors 720 and 724, forinstance. The coupling network 850 is analogous to the coupling network610 of FIG. 6 a. In another possible option, the chip set 614 can bereplaced by the chips 654 and 650 of FIG. 6 b. DC power form the PSU 854is provided to the coupling network 850 via terminals 852, 854 and 856.Specifically, a positive potential (VDC+), a ground potential (0 V) anda negative potential (VDC−) are provided to the terminals 852, 854 and856, respectively. Many other implementations are possible.

FIG. 9 a depicts an exemplary routing table, and FIGS. 9 b and 9 cdepict routing of a packet between user stations using the routing tableshown in FIG. 9 a. Generally, selective communication of audio packetsover a digital network can be achieved by assigning IP addresses orother network addresses or identifiers to the user stations, andassigning the user stations to groups or sessions based on theirrespective network addresses. Moreover, one or more of such groups orsessions can be defined and can be concurrently active. For example, therouter 816 of a master station may maintain a routing table for aparticular session, session 1, which associates one or more networkaddresses of talker user stations with one or more network addresses oflistener user stations. The router 816 can be configured with thesession such as by connecting a computing device to the master stationwhich has a GUI which allows a user to configure the appropriatesettings. In another approach, the master station is updated remotelysuch as via a web-based GUI. FIG. 9 a illustrates that the talkers areassociated with user stations having network addresses of IP2 and IP3and the listeners are associated with user stations having networkaddresses IP2 and IP4.

As depicted in FIG. 9 b, when a user speaks into the user stationassociated with IP2, the user station transmits audio by sending digitalpackets to the master station 900, which identifies the sender's addressIP2 and an address IP5 of the master station 900 as the recipient. Therouter at the master station identifies IP2 as the address associatedwith the sender/talker, and determines which user stations are listenersfor a current session. The packets are routed from the master station tothe user station of IP4 based on the routing table, allowing the useroperating the user station associated with IP4 to hear the user talk. Inparticular, the router can send packets from the master station to theuser station of IP4 which identify IP4 as the recipient and the masterstation IP5 as the sender. The IP4 user station receives the digitalpackets from the master station and converts them to an analog audiooutput. The other user stations examine the packets to determine thatthey are not addressed to them and do not retrieve them. In this case,there is only one recipient, in a point-to-point communication.

In FIG. 9 c, the IP3 user station is the sending device. The routing DSPat the master station identifies IP3 as the address of thesender/talker, and determines which user stations are listeners for acurrent session. From the routing table of FIG. 9 a, IP2 and IP4 areaddresses of listeners. The packets are thus routed to the IP2 and IP4user stations as listeners, so that the associated user can hear theuser associated with the IP3 user station talk. In particular, therouter can send packets from the master station which identify IP2 andIP4 as the recipients and the master station IP5 as the sender. In thiscase, there are multiple recipients, in a point-to-multi pointcommunication.

In routing, the packets can be numbered so that the master station or adestination user station can tell whether it received all the packetsintended for it, and if it does not receive some packets, it can reportback to any element of the system so that the problem can be noted.

FIG. 10 a depicts another exemplary routing table, and FIG. 10 b depictsrouting of a packet between user stations using the routing table shownin FIG. 10 a. This case represents point-to-multi point communicationand party line communication. A party line communication from one userstation can be heard by all other user stations in the intercom network.Here, the routing table identifies all other addresses (IP1, IP2 andIP4) when the user associated with the IP3 user station is talking.Alternatively, a wild card can be used in a packet which indicates thatall user stations are to retrieve the packet.

In FIG. 10 b, the IP3 user station sends a packet to the master station1000. The router at the master station routes the packet for retrievalby the associated IP1, IP2 and IP4 user stations, and the master stationis identified as the sender.

FIG. 1 a depicts an exemplary table of listener user stations, and FIG.11 b depicts forwarding of a packet using the table. In this case, theuser stations have the intelligence to know the group or session inwhich they are participating. For example, the user stations can beconfigured with such information, such as by connecting each userstation manually to a computing device which programs in thecorresponding group or session information, or automatically such as byreceiving the configuration information as control data from the masterstation. Thus, a routing capability is not needed at the master station.Instead, the master station forwards the packets in the same networkfrom which they were received and/or one or more other networks. Forexample, for a “user station 4,” having a unique identifier IP4, theunique identifiers of other intercoms for which user station 4 is alistener are IP1 and IP2. Thus, the IP4 user station will listen to theIP1 and IP2 user stations, but not to other user stations.

In FIG. 11 b, the IP2 user station sends audio packets with IP2 as thesender's identifier on the network. The master station 110 forwards thepackets back onto the same or a different network, keeping IP2 as thesender's identifier. The IP4 user station examines the packets todetermine the sender's identifier, and uses the table of listener userstations to determine that it is a listener for the packet. The IP4 userstation retrieves the digital packets for which it is a listener andconverts them to an analog audio output. The other user stations examinethe packets similarly to determine whether or not to retrieve them. Inthis case, a user station can retrieve a packet even if it is notforwarded by the master station but is received directly from thesending user station in the same network.

FIG. 12 a depicts an exemplary first process for selectivelycommunicating data packets among user stations. The examples of FIGS. 9a-10 b are compatible with this process. Generally, this processinvolves each user station connecting to the master station, such aswhen the user station is powered on, to obtain an identifier and sessioninformation. For example, at step 1200, the user station connects to themaster station to obtain a unique identifier. The user station mayoptionally provide credentials which allow it to securely login to thenetwork. Encryption may also be used to enhance security.

At step 1202, the user station obtains a list of available sessions fromthe master station. At step 1204, the user station sends a request tojoin one or more sessions, based on preconfigured settings of the userstation or based on a user selection, for instance. At this point, theuser station is configured and ready to begin communicating audio toother user stations, when the user desires to talk. At step 1206, theuser talks, and the user station communicates audio packets with itsunique identifier to the master station. At step 1208, the masterstation determines one or more sessions which the user station hasjoined. At step 1210, the master station determines the uniqueidentifiers of listener user stations in the one or more sessions. Atstep 1212, the master station routes packets to the listener userstations using their identifiers.

FIG. 12 b depicts an exemplary second process for selectivelycommunicating data packets among user stations. The examples of FIGS. 9a-10 b are compatible with this process. At step 1220, the user stationis configured with a unique identifier. At step 1222, the master stationis configured with sessions, where each session identifies talking andlistening user stations. At step 1224, the user station communicatesaudio packets with its unique identifier to the master station. At step1226, the master station determines one or more sessions to which theuser station has been assigned. At step 1228, the master stationdetermines the unique identifiers of listener user stations in the oneor more sessions. At step 1230, the master station routes packets to thelistener user stations using their identifiers.

FIG. 12 c depicts an exemplary third process for selectivelycommunicating data packets among user stations. The examples of FIGS. 11a and 11 b are compatible with this process. At step 1250, each userstation is configured with a unique identifier and a list of uniqueidentifiers of other user stations for which it is a listener. At step1252, a user station communicates audio packets with its uniqueidentifier on the network. At step 1254, the master station forwards thepackets to other user stations in the same and/or different networks. Atstep 1256, the other user stations listen to packets if the packet'sunique identifier is on their respective list of other user stations forwhich it is a listener.

FIG. 13 depicts an exemplary process for retrofitting an analog intercomnetwork to provide a digital communication capability. As mentioned atthe outset, the techniques and systems provided herein allow easyretrofitting of existing analog intercom networks with digital equipmentto provide full featured, multi-channel digital communications overexisting cabling. In a corresponding retrofitting process, step 1300includes beginning the retrofit of an existing analog network. Step 1302includes disconnecting the existing analog master station and analoguser stations from the cable network. This can simply involvedisconnecting the XLR or other cable connectors. Step 1304 includesconnecting a digital master station and digital user stations to thecable network. This can simply involve reconnecting the XLR or othercable connectors. Step 1306 includes providing DC power from the digitalmaster station to the digital user stations via the cable network. Step1308 includes providing bidirectional digital communications among thedigital master station and the digital user stations in the cablenetwork, including routing and/or forwarding of digital data packets.The bidirectional (two-way) digital communications can occurconcurrently or at different times.

The foregoing detailed description of the invention has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed. Manymodifications and variations are possible in light of the aboveteaching. The described embodiments were chosen in order to best explainthe principles of the invention and its practical application, tothereby enable others skilled in the art to best utilize the inventionin various embodiments and with various modifications as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto.

1. A digital intercom network, comprising: a cable network comprising atleast one cable, the at least one cable comprising first, second andthird conductive paths, the third conductive path is a ground path; atleast one user station connected to the first, second and thirdconductive paths; and a master station comprising: a DC power supplyconnected to the first, second and third conductive paths, the DC powersupply powers the at least one user station; a transceiver whichprovides bidirectional digital communications in at least three channelsvia the first, second and third conductive paths, including transmittingdigital signals concurrently via the first, second and third conductivepaths, and receiving signals concurrently via the first, second andthird conductive paths; and a router in communication with thetransceiver, the router routes digital data packets in the at leastthree channels.
 2. The digital intercom network of claim 1, wherein: theDC power supply provides a positive potential relative to the groundpath on the first conductive path, and a negative potential relative tothe ground path, of equal magnitude to the positive potential, on thesecond conductive path; and the transceiver transmits and receivesdifferential signals via the first, second and third conductive paths.3. The digital intercom network of claim 1, wherein: the at least oneuser station is connected to the at least one cable via a drop cable,the drop cable connects to the at least one cable without using activeelectronic components.
 4. The digital intercom network of claim 1,wherein: the at least one cable is a shielded audio microphone cable inwhich the first and second conductive paths are provided by a twistedpair of wires and the ground path comprises a shield.
 5. The digitalintercom network of claim 4, wherein: the at least one cable comprisesan XLR connector which connects to the master station.
 6. The digitalintercom network of claim 1, wherein: the at least one cable has anauxiliary conductive path to the first conductive path and an auxiliaryconductive path to the second conductive path, a positive terminal ofthe DC power supply is connected to the first conductive path and itsauxiliary conductive path, and a negative terminal of the DC powersupply is connected to the second conductive path and its auxiliaryconductive path, so that the DC power supply powers the at least oneuser station via the first and second conductive paths and theirauxiliary conductive paths.
 7. The digital intercom network of claim 6,wherein: the transceiver provides bidirectional digital communicationsusing one signal on both the first conductive path and its auxiliaryconductive path, and another signal on both the second conductive pathand its auxiliary conductive path.
 8. The digital intercom network ofclaim 1, wherein: the master station is connected to opposing ends ofthe at least one cable so that the cable network comprises a ringtopology.
 9. The digital intercom network of claim 1, wherein: therouter routes digital data packets among user stations according to oneor more sessions with which the user stations are associated, based onrespective network addresses of the user stations.
 10. The digitalintercom network of claim 9, wherein: the one or more sessions identifythe at least one user station as a talker, and at least one other userstation as a listener.
 11. A master station for use in a digitalintercom network, the master station comprising: a first connector whichis connected to at least first, second and third conductive paths of atleast one cable of the digital intercom network, the third conductivepath is a ground path; a DC power supply connected to the at leastfirst, second and third conductive paths via the first connector, the DCpower supply powers at least one user station which is connected to theat least one cable; a transceiver which provides bidirectional digitalcommunications with the user stations in at least three channels via theat least first, second and third conductive paths, includingtransmitting digital signals concurrently via the at least first, secondand third conductive paths, and receiving signals concurrently via theat least first, second and third conductive paths; and a router incommunication with the transceiver, the router routes digital datapackets in the at least three channels to provide digitalpoint-to-point, digital point-to-multi-point, and digital party linecommunications among the user stations.
 12. The master station of claim11, wherein: the at least one cable is a shielded audio microphone cablein which the first and second conductive paths are provided by a twistedpair of wires and the ground path comprises a shield.
 13. The masterstation of claim 11, wherein: the DC power supply provides a positivepotential relative to the ground path on the first conductive path, anda negative potential relative to the ground path, of equal magnitude tothe positive potential, on the second conductive path; and thetransceiver transmits and receives differential signals via the first,second and third conductive paths.
 14. The master station of claim 11,wherein: the router routes digital data packets among user stationsaccording to one or more sessions with which the user stations areassociated, based on respective network addresses of the user stations.15. The master station of claim 14, wherein: the one or more sessionsidentify the at least one user station as a talker, and at least oneother user station as a listener.
 16. A user station in a digitalintercom network provided over at least one cable, the user stationcomprising: an interface to the at least one cable, the at least onecable comprising at least first, second and third conductive paths, thethird conductive path is a ground path; a power conversion unitassociated with the interface for receiving DC power from the at leastfirst, second and third conductive paths; and a transceiver whichprovides bidirectional digital communications via the at least first,second and third conductive paths, including transmitting digitalsignals concurrently via the at least first, second and third conductivepaths, and receiving signals concurrently via the at least first, secondand third conductive paths, wherein the bidirectional digitalcommunications are provided via at least one channel of at least threeavailable channels which are provided over the at least first, secondand third conductive paths.
 17. The user station of claim 16, wherein:the interface is connected to the at least one cable via a drop cable,the drop cable connects to the at least one cable without using activeelectronic components.
 18. The user station of claim 16, wherein: thetransceiver receives digital data packets which are routed to the userstation using a respective network address, according to an associatedsession in which the user station is a listener and at least one otheruser station is a talker.
 19. A method for retrofitting an analogintercom network to provide a digital communication capability, theanalog intercom network includes analog user stations, an analog masterstation and a cable network comprising at least one cable, the at leastone cable has first, second and third conductive paths, the thirdconductive path is a ground path, the method comprising: disconnectingthe analog user stations and the analog master station from the at leastone cable; connecting digital user stations to the at least one cable inplace of the analog user stations; and connecting a digital masterstation to the at least one cable in place of the analog master station,the digital master station: (a) provides DC power to the at least first,second and third conductive paths, the DC power is sufficient to powerthe user stations, and (b) provides bidirectional digital communicationsin at least three channels via the first, second and third conductivepaths, including transmitting digital signals concurrently via thefirst, second and third conductive paths, and receiving signalsconcurrently via the first, second and third conductive paths, where theproviding bidirectional digital communications includes routing digitaldata packets at the digital master station in the at least threechannels to provide digital point-to-point, digitalpoint-to-multi-point, and digital party line communications among theuser stations according to respective network addresses of the userstations.
 20. The method of claim 19, wherein: at least one of thedigital user stations is connected to the at least one cable via a dropcable, the drop cable is connected to the at least one cable withoutusing active electronic components.